Additional references (will be added to upstream once more references can be handled)

Reference:
 - Author: Bacon, D.J., & Anderson, W.F.
   Title: A Fast Algorithm for Rendering Space-Filling Molecule Pictures
   Year: 1988
   Journal: J. Molec. Graphics
   Volume: 6
   Pages: 219-220
 - Author: Kraulis, P.J.
   Title: "MOLSCRIPT: a program to produce both detailed and schematic plots of protein structures"
   Year: 1991
   Journal: J. Appl. Cryst.
   Volume: 24
   Pages: 946-950
 - Author: Merritt, E.A. & Murphy, M.E.P.
   Title: Raster3D Version 2.0 - A Program for Photorealistic Molecular Graphics
   Year: 1994
   Journal: Acta Cryst.
   Volume: D50
   Pages: 869-873.
